So @Endri asks if we're missing something. Are we? Let's go through it all again then.
We have to
The Mountaineers must use the most dangerous of magiq
The Mountaineers must reach out to the past
We have a chronocompass on Fletcher's site.
We have a chronocompass in Deidre's hands pointing to Gossmere. (OR Thornmouth some suggest.)
We have the name Neithernor.
We have a blank journal.
We are missing something or not realizing the significance of something.
Unless Sullivan is expecting us to make up a time travel spell on our own to an vaguely defined point of time in the past... In which case I vote no. I've seen enough bad sci fi to know that's not a good idea.